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The identification of groundwater contamination sources (IGCSs) is an important requirement for the remediation and treatment of groundwater contamination. The data assimilation methods such as ensemble Kalman filter (EnKF) and ensemble smoother (ES) have been applied to IGCSs in recent years and obtained good identification results. The unscented kalman filter (UKF) is also a data assimilation method with the potential to simultaneously identify hydraulic conductivity and GCSs. However, when UKF is applied to identify hydraulic conductivity and GCSs, it is necessary to use the observed data at different times separately, which increases the complexity of the update process and this may result in low identification accuracy. ES is a variant of EnKF that updates the system parameters with all observed data in all time periods, which makes ES faster and easier to implement than EnKF. Therefore, inspired by the ES, an unscented kalman smoother (UKS) based on UKF was proposed for simultaneously identifying the hydraulic conductivity and GCSs in this study. The UKS can use the data observed in all time periods simultaneously, while it is also simpler to operate and the calculation speed is faster. Present studies have shown that ES can solve IGCS problems. Thus, ES was also applied to identify the hydraulic conductivity and GCSs in this study, and its identification performance was compared with UKS. In contrast to previous applications of ES to IGCSs, both UKS and ES were set up with stop iteration conditions instead of only performing one update process, and thus both methods applied multiple update processes. The results showed that compared with ES, the identification results obtained by UKS were characterized by greater stability, higher accuracy, and the iterative process required less iteration process and computational time. [ABSTRACT FROM AUTHOR]

The issues associated with long‐screened wells (LSWs) (and open boreholes) at contaminated sites are well documented in the groundwater literature but are still not fully appreciated in practice. As established in seminal and review papers going back over three decades, the interpretation of sampling results from LSWs is challenging in the presence of vertical hydraulic gradients and borehole flow; furthermore, LSWs allow for vertical redistribution of contamination between aquifer layers. Acknowledgment of these issues has led to the development of new technologies and well designs to enable discrete‐zone monitoring (DZM), yet LSWs remain common for many reasons, for example, as multipurpose wells, for geophysical logging, and (or) as legacy installations. Despite the literature on LSWs and despite the adoption of DZM at many sites, the use of LSWs persists and the challenges of interpreting sampling results from LSWs remain. In this issue paper, we provide a conceptual overview of the problems posed by LSWs and review existing literature and past work to improve the interpretation of sampling in LSWs. We draw on experience from previous studies at the Hanford Site in eastern WA, USA, and use synthetic examples to illustrate key concepts and challenges for interpretation. A recently published analytical modeling framework is used to develop illustrative synthetic examples and demonstrate a workflow for building scientific intuition to understand issues around interpreting samples from LSWs, which is critical to effective characterization and groundwater remediation at sites with LSWs. [ABSTRACT FROM AUTHOR]

Pump‐and‐treat technologies are widely used in groundwater remediation and site cleanup. Such technologies involve pumping contaminated groundwater to the surface for treatment. Following treatment, the water is often reinjected back into the aquifer (referred to as pump‐treat‐inject or PTI) for potential reuse. The treatment system is often designed to remove dissolved‐phase contaminants in groundwater such that water meets applicable cleanup standards (herein referred to as "full treatment"). However, in some cases, the treatment system may not effectively reduce the dissolved‐phase concentrations (herein referred to as "partial treatment") for some of the contaminants present in groundwater. Modeling PTI under partial treatment conditions is challenging because contaminant concentrations in injected water depend on the pumped water concentrations and the system treatment efficiency. Essentially, the injected water concentration (a transport model input) is unknown prior to transport simulation. This study presents a novel iterative approach to modeling PTI under partial treatment scenarios, where the injected water concentration is linked to the modeled pumped water concentration. The method was developed for a complicated three‐dimensional (3D) flow and transport modeling study conducted for a confidential remediation site where PTI with partial treatment was applied. However, due to the complexity of the 3D model and the confidential information of the site, a simple two‐dimensional (2D) numerical model is presented to demonstrate the iterative method. The 2D model test runs and the 3D model application in a remediation site showed that the iterative simulation results quickly converged to a viable final solution. [ABSTRACT FROM AUTHOR]

Identifying highly channelized hydraulic conductivity fields and contaminant source parameters remains a challenging task, primarily due to the non‐Gaussian nature and high dimensionality of the parameter space, as well as the computational burden caused by repeatedly running forward numerical models. This study proposes a novel deep learning parameterization method called AEdiffusion, which combines Diffusion Denoising Probabilistic Model (DDPM) with Variational Autoencoder (VAE) for dimensionality reduction. The method employs a generator‐refiner strategy to generate high‐dimensional aquifer properties from low‐dimensional latent representations. The inversion modeling was performed on a synthetic non‐Gaussian hydraulic conductivity field with line‐source contamination using the Iterative Local Updating Ensemble Smoother (ILUES) algorithm. The results demonstrate that the AEdiffusion‐ILUES framework can accurately identify model parameters. To reduce the computational burden, an AR‐Net‐WL (ARNW) surrogate model was introduced, resulting in an efficient inversion framework (AEdiffusion‐ILUES‐ARNW) with similar prediction accuracy and predictive uncertainty estimation as the AEdiffusion‐ILUES but at a lower computational cost. Plain Language Summary: Identifying highly channelized hydraulic conductivity fields and contaminant source parameters is crucial for developing groundwater remediation strategies. However, this remains a challenging task due to the non‐Gaussian nature and high dimensionality of the parameter space, as well as the computational burden caused by repeatedly running numerical models. We propose a novel deep learning‐based inversion framework to identify hydraulic conductivity fields and contaminant sources from sparse and error‐prone observations. Key Points: A novel and accurate deep learning parameterization method combining DDPM and VAE is proposed to parameterize non‐Gaussian hydraulic conductivity fieldsA deep autoregressive neural network is integrated into the inversion framework as a surrogate to alleviate the high computational cost of the forward numerical modelsThe integrated approach is assessed with inverse problems for the identification of a non‐Gaussian conductivity and line contaminant source parameters [ABSTRACT FROM AUTHOR]

The extensive use of methyl tert-butyl ether (MTBE) as a gasoline additive has caused serious environmental problems that need to be addressed urgently. The feasibility of remediation of MTBE-contaminated groundwater by ZSM-5 zeolite with SiO2/Al2O3 ratio of 50/130/360 was explored. The SiO2/Al2O3 ratio had a great influence on the physicochemical properties and structure, as well as the adsorption and mass transfer of MTBE on ZSM-5. The adsorption of MTBE on zeolites with SiO2/Al2O3 ratios of 50 and 130/360 followed the Langmuir and Freundlich models, respectively, and was controlled by different mass transfer processes. The morphology and adsorption capacity of ZSM-5 (50) and ZSM-5 (130) differed significantly, while the differences between ZSM5-(130) and ZSM-5 (360) were less pronounced. ZSM-5 (360) had higher adsorption capacity and adsorption efficiency for MTBE, and the larger BET surface area, pore volume and stronger hydrophobicity were the key factors to promote MTBE adsorption. Compared to activated carbon (AC), ZSM-5 (360) was more effective for MTBE removal at low concentrations (<200 mg-L-1) and had the advantage of selective adsorption of MTBE with the addition of BTEX. In column adsorption, decreasing the concentration had opposite effects on MTBE removal by ZSM-5 and AC. At 5-10 mg-L-1, ZSM-5 (360) column reduced effluent concentration and improved bed utilization and removal efficiency. [ABSTRACT FROM AUTHOR]

Excessive dense nonaqueous phase liquids (DNAPLs) in subsurface aquifers posed a threat to human health and sustainable development of groundwater resources. Accurately identifying the sources of DNAPLs is crucial for groundwater remediation and prevention efforts. In the previous studies, significant advances were made in using isotope techniques for identifying DNAPLs in groundwater. In this paper, we provide a comprehensive overview of the commonly used isotopic tools applied to source identification. This overview will outline the advantages and limitations of the isotope technique and describe the needs for future research. Isotope tracing techniques are based on the unique isotopic characteristics of DNAPLs from different sources, enabling the identification and differentiation of DNAPL sources. The δ13C and δ37Cl values are most commonly used for identifying DNAPLs in groundwater. In field applications, however, the differences in isotopic characteristics from diverse sources can be weakened after undergoing a series of human and natural factors, which can affect the accuracy of source identification. To improve the accuracy of DNAPL source identification, a dual-isotope tracing approach seems the best available solution. Nonetheless, in the face of complex polluted environments, the dual-isotope method seems stretched. Therefore, further researches remain to be carried out to accurately and efficiently assess the sources of DNAPLs in groundwater and their individual contributions. This is a prerequisite for groundwater resource conservation and remediation efforts. [ABSTRACT FROM AUTHOR]

Sulphidation of nZVI (S-nZVI) has shown to significantly improve the arsenic removal capacity of nZVI, concurrently modifying the sequestration mechanism. However, to better apply S-nZVI for groundwater arsenic remediation, the impact of groundwater coexisting ions on the efficacy of arsenic uptake by S-nZVI needs to be investigated. This present study evaluates the potential of S-nZVI to remove arsenic in the presence of typical groundwater coexisting ions such as Cl−, HA, HCO3−, PO43− and SO42− through batch adsorption experiments. Individually, PO43− and HA had a dominant inhibition effect, while SO42− promoted As(III) removal by S-nZVI. Conversely, for As(V) removal, HCO3− and SO42− impeded the removal process. X-ray spectroscopic investigation suggests that the coexisting ions can either compete with arsenic for the adsorption sites, influence the S-nZVI corrosion rates and/or generate distinct corrosion products, thereby interfering with arsenic removal by S-nZVI. To investigate the cumulative effects of these ions, a 25–1 Fractional Factorial Design of experiments was employed, wherein the concentration of all the ions were varied simultaneously in an optimized manner, and their impact on arsenic removal by S-nZVI was observed. Our results shows that when these ions are present concurrently, PO43−, SO42− and HA still exerted a dominant influence on As(III) removal, whereas HCO3− was the main ions affecting As(V) removal, although the combined influence of the ions was not merely a summation of their individual effects. Overall, the finding of our study might provide valuable insight for predicting the actual performance of S-nZVI in field-scale applications for the remediation of arsenic-contaminated groundwater. [ABSTRACT FROM AUTHOR]

This study explores the use of pine wood biochar (BC) waste gasified at 950 °C as fillers in polymer matrices to create BC@biopolymer composites with perspectives in groundwater remediation. Four biochar samples underwent different sieving and grinding processes and were extensively characterized via UV–Vis, FTIR, and FESEM–EDS, highlighting the fact that that BCs are essentially graphitic in nature with a sponge-like morphology. The grinding process influences the particle size, reducing the specific surface area by about 30% (evaluated by BET). The adsorption performances of raw BC were validated via an adsorption isotherm using trichloroethylene (TCE) as a model contaminant. A selected BC sample was used to produce hydrophilic, stable polymer composites with chitosan (CS), alginate (ALG), potato starch (PST), and sodium carboxymethylcellulose (CMC) via a simple blending approach. Pilot sedimentation tests over 7 days in water identified BC@PST and BC@CMC as the most stable suspensions due to a combination of both hydrogen bonds and physical entrapment, as studied by FTIR. BC@CMC showed optimal distribution and retention properties without clogging in breakthrough tests. The study concludes that biopolymer-based biochar composites with improved stability in aqueous environments hold significant promise for addressing various groundwater pollution challenges. [ABSTRACT FROM AUTHOR]

With the increasing environmental impacts of human activities, the problem of polygenic multipollutants in groundwater has attracted the attention of researchers. Identifying the hydrobiogeochemical characteristics of the surface sewage that replenishes groundwater is crucial to addressing this problem. The input of polygenic multipollutants into groundwater leads to not only the mechanical superposition of pollutants but also the formation of secondary pollutant types. The evolution of polygenic multipollutants is influenced by aquifer characteristics, carbon sources, microbial abundance, etc. Therefore, this study took a sewage leakage point in Northwest China as the research object, carried out a controlled laboratory experiment on the impact of sewage discharge on groundwater, and, combined with long-term field monitoring results, determined the main hydrobiogeochemical processes of polygenic multipollutants and their secondary pollutants. The results showed that the redox environment and the gradient change in pH were identified as the most critical controlling factors. In oxidative groundwater during the early stage of vertical infiltration, sewage carries a substantial amount of NH4+, which is oxidized to form the secondary pollutant NO3−. As O2 is consumed, the reduction intensifies, and secondary pollutants NO3−, Mn (IV), and Fe(III) minerals are successively reduced. Compared with the natural conditions of rainwater vertical infiltration, the reaction rates and intensities of various reactions significantly increase during sewage vertical infiltration. However, there is a notable difference in the groundwater pH between sewage and rainwater vertical infiltration. In O2 and secondary pollutant NO3− reduction, a large amount of CO2 is rapidly generated. Excessive CO2 dissolves to produce a substantial amount of H+, promoting the acidic dissolution of Mn (II) minerals and generation of Mn2+. Sewage provides a higher carbon load, enhancing Mn (II) acidic dissolution and stimulating the activity of dissimilatory nitrate reduction to ammonium, which exhibits a higher contribution to NO3− reduction. This results in a portion of NO3− converted from NH4+ being reduced back to NH4+ and retained in the groundwater, reducing the denitrification's capacity to remove secondary NO3−. This has important implications for pollution management and groundwater remediation, particularly monitored natural attenuation. [ABSTRACT FROM AUTHOR]

Impermeability and water blocking are crucial for remediating shallow groundwater contamination. Traditional methods often employ curtain-grouting technology to create impermeable layers. However, cement slurry curing is irreversible, leading to permanent closure of underground aquifers and secondary pollution. This study employs an innovative approach by fabricating cylindrical models that simulate actual strata and utilizing a high-temperature and high-pressure displacement device. It systematically analyzes the variations in soil pore structure, distribution, porosity, and permeability under different temperatures, pressures, and freezing durations. The microscopic characteristics of the freezing process in water-bearing soils were studied. Results demonstrate that longer freezing time improves the effectiveness of soil freezing, reaching complete freezing at temperatures as low as −4 °C for samples with low water content. For water-saturated samples, freezing below −6 °C results in nearly zero porosity. Increased pressure at a certain freezing temperature significantly reduces permeability. When freezing temperature falls below −4 °C, water permeability in saturated samples after freezing reaches near-zero levels, while unsaturated samples experience complete freezing. These findings provide a theoretical foundation for constructing freezing curtains in remediating shallow groundwater pollution. [ABSTRACT FROM AUTHOR]

In-situ chemical oxidation with persulfate (PS-ISCO) is a preferred approach for the remediation of fuel-contaminated groundwater. Persulfate (PS) can be activated by various methods to produce stronger sulfate radicals for more efficient ISCO. Despite karst aquifers being widespread, there are few reports on PS-ISCO combined with Fe2+-activated PS. To better understand the effects of Fe2+-activated PS for the remediation of gasoline-contaminated aquifers in karst areas, a box-column experiment was conducted under flow conditions, using karst groundwater and limestone particles to simulate an aquifer. Gasoline was used as the source of hydrocarbon contaminants. Dissolved oxygen and nitrate were added to enhance bioremediation (EBR) and ferrous sulfate was used to activate PS. The effect of Fe2+-activated PS combined with biodegradation was compared during the periods of EBR + ISCO and ISCO alone, using the mass flow method for data analysis. The results showed that the initial dissolution of benzene, toluene, and xylene (BTX) from gasoline injection was rapid and variable, with a decaying trend at an average pseudo-first-order degradation rate constant of 0.032 d−1. Enhanced aerobic biodegradation and denitrification played a significant role in limestone-filled environments, with dissolved oxygen and nitrate utilization ratios of 59 ~ 72% and 12–70%, respectively. The efficiency of EBR + ISCO was the best method for BTX removal, compared with EBR or ISCO alone. The pseudo-first-order degradation rate constants of BTX reached 0.022–0.039, 0.034–0.070, and 0.027–0.036 d−1, during the periods of EBR alone, EBR + ISCO, and ISCO alone, respectively. The EBR + ISCO had a higher BTX removal ratio range of 71.0 ~ 84.3% than the ISCO alone with 30.1 ~ 45.1%. The presence of Fe2+-activated PS could increase the degradation rate of BTX with a range of 0.060 ~ 0.070 d−1, otherwise, with a range of 0.034–0.052 d−1. However, Fe2+-activated PS also consumed about 3 times the mass of PS, caused a further decrease in pH with a range of 6.8–7.6, increased 3–4 times the Ca2+ and 1.6–1.8 times the HCO3− levels, and decreased the BTX removal ratio of ISCO + EBR, compared to the case without Fe2+ activation. In addition, the accumulation of ferric hydroxides within a short distance indicated that the range of PS activated by Fe2+ may be limited. Based on this study, it is suggested that the effect of Fe2+-activated PS should be evaluated in the remediation of non-carbonate rock aquifers. [ABSTRACT FROM AUTHOR]

This paper provides an introduction to groundwater PRE technology, in situ bioremediation technology, and in situ chemical oxidation technology. It also presents a summary of the core-shell structure and physical and chemical preparation methods of nZVI. Furthermore, it discusses the mechanism by which nZVI degrades heavy metals, non-metallic inorganic substances, halogenated organics, and antibiotics in groundwater through processes such as adsorption/reduction, precipitation etc. The interaction mechanism between nZVI and microorganism coupling system is described along with an analysis of the promoting and inhibiting effects that nZVI has on microorganisms. Additionally, the research progress on removing groundwater pollutants using coupling systems is discussed. Finally, the future research focus for coupling technologies is proposed. [ABSTRACT FROM AUTHOR]

In this work, we build upon our previous finding that hydrodynamic porosity is an exponential function of pore-scale flow velocity (or interstitial Reynolds number). We previously discovered this relationship for media with a square cavity geometry—a highly idealized case of the dead-ended pore spaces in a porous medium. Thus, we demonstrate the applicability of this relationship to media with other cavity geometries. We do so by applying our previous analysis to rectangular and non-rectangular cavity geometries (i.e., circular, and triangular). We also study periodic flow geometries to determine the effect of upstream cavities on those downstream. We show that not only does our exponential relationship hold for media with a variety of cavity geometries, but it does so almost perfectly with a coefficient of determination (R2) of approximately one for each new set of simulation data. Given this high fit quality, it is evident that the exponential relationship we previously discovered is applicable to most, if not all, unwashed media. [ABSTRACT FROM AUTHOR]

• Combined with the actual site groundwater characteristics. • Discussed the design of MFCs, including configuration and size, electrode, membranes and separators, contaminants. • Reviewed the progress of research on groundwater removal with MFCs in the last decade. • Considerd the efficiency and practicability of MFCs. Microbial fuel cells (MFCs) have become more prevalent in groundwater remediation due to their capacity for power generation, removal of pollution, ease of assembly, and low secondary contamination. It is currently being evaluated for practical application in an effort to eliminate groundwater pollution. However, a considerable majority of research was conducted in laboratories. But the operational circumstances including anaerobic characteristics, pH, and temperature vary at different sites. In addition, the complexity of contaminants and the positioning of MFCs significantly affect remediation performance. Taking the aforementioned factors into consideration, this review summarizes a bibliography on the application of MFCs for the remediation of groundwater contamination during the last ten decades and assesses the impact of environmental conditions on the treatment performance. The design of the reactor, including configuration, dimensions, electrodes, membranes, separators, and target contaminants are discussed. This review aims to provide practical guidance for the future application of MFCs in groundwater remediation. [Display omitted] [ABSTRACT FROM AUTHOR]

• A CO 2 combined oxidant method for PRB regeneration is proposed for leachate–contaminated areas near landfill. • CO 2 well-washing technology is used for improving PRBs permeability. • The optimal ratios of oxidants and PRB fillers are proposed to achieve the best regeneration effect. Groundwater contamination near landfills is commonly caused by leachate leakage, and permeable reactive barriers (PRBs) are widely used for groundwater remediation. However, the deactivation and blockage of the reactive medium in PRBs limit their long-term effectiveness. In the current study, a new methodology was proposed for the in situ regeneration of PRB to remediate leachate-contaminated groundwater. CO 2 coupled with oxidants was applied for the dispersion and regeneration of the fillers; by injecting CO 2 to disperse the fillers, the permeability of the PRB was increased and the oxidants could flow evenly into the PRB. The results indicate that the optimum filler proportion was zero-valent iron (ZVI)/zeolites/activated carbon (AC) = 3:8:10 and the optimum oxidant proportion was COD/Na 2 S 2 O 8 /H 2 O 2 /Fe2+ = 1:5:6:5; the oxidation system of Fe2+/H 2 O 2 /S 2 O 8 2− has a high oxidation efficiency and persistence. The average regeneration rate of zeolites was 72.71%, and the average regeneration rate of AC was 68.40%; the permeability of PRB also increased. This technology is effective for the remediation of landfills in China that have large contaminated areas, an uneven pollutant concentration distribution, and a long pollution duration. The purification mode of long-term adsorption and short-time in situ oxidation can be applied to the remediation of long-term high-concentration organically polluted groundwater, where pollution sources are difficult to cut off. [ABSTRACT FROM AUTHOR]

Fe(II) is of great importance in iron-based advanced oxidation processes. However, traditional methods to maintain Fe(II) concentration, such as the addition of chelating agents or reducing agents, may lead to an increase in chemical oxygen demand of secondary pollution. Therefore, in this study, iron sulfides, namely ferrous sulfide (FeS), pyrite (FeS2), and sulfidated nanoscale zero-valent iron (S-nZVI), were applied for not only the regeneration of Fe(II) but also the direct dissolution of Fe(II). Nanoscale calcium peroxide (nCaO2) was synthesized and used as the oxidant. The removal of 1,2-dichloroethane (1,2-DCA) were significantly promoted from 8.8 to 98.2, 79.2, and 80.8% with the aid of FeS, FeS2, and S-nZVI within 180 min, respectively. The dominant reactive oxygen species were demonstrated and their steady-state concentrations were quantified. Besides, the dechlorination of 1,2-DCA reached 90.4, 69.5, and 83.9% in nCaO2/Fe(III) systems coupled with FeS, FeS2, and S-nZVI, respectively. All three systems had high tolerance to the complex water conditions, of which FeS-enhanced nCaO2/Fe(III) system displayed the best performance, which could be recommended to put into practice for the remediation of 1,2-DCA contaminated groundwater. HIGHLIGHTS FeS, FeS2, and S-nZVI were applied for the enhancement of nCaO2/Fe(III) system.; The advantages of nCaO2 toward commercial CaO2 were elucidated.; The dominant ROS and their steady-state concentrations were determined.; The effect of complex solution matrixes on the performance of enhanced systems was investigated.; The universality on the removal of other typical contaminants was inspected.;

Pyrite is a ubiquitous sulfide mineral found in diverse geological settings and holds great significance in the formation of Au deposits as well as the safe utilization of groundwater due to its remarkable ability to incorporate substantial amounts of As. However, despite its importance, there remains a dearth of fundamental data on the partitioning of As between pyrite and fluid, which is key for accurately modeling the As distribution in these environments. Here, we present new insights into the partitioning behavior of As between pyrite and fluid at conditions that mimic natural fluid systems. Pyrite was synthesized by replacement of natural siderite in hydrothermal experiments at 200 °C and pH 5 applying a wide range of fluid As concentrations, spanning from 0.001 to 100 µg/g. The As distribution and concentration in synthetic pyrite was analyzed by quantitative LA-ICP-MS mapping providing a high spatial resolution and sensitivity at 2–3 µm image pixel size at a detection limit of ∼1 µg/g at the single pixel scale. Pyrite-fluid partitioning coefficients (D As (py/fluid)) between synthetic pyrite and experimental fluid agree with previously published data for high fluid As concentrations of 1 µg/g to 100 µg/g (D As < 2000). However, at low As concentrations in the experimental fluid (<1 µg/g), a steep increase in the D As (py/fluid) values of up to ∼30,000 was detected, demonstrating even stronger As partitioning into pyrite. This is confirmed by the analyses of natural pyrite that precipitated from As-poor fluids (0.3–0.4 ng/g) within a deep anoxic aquifer in SE Sweden. The discovery holds significant implications for the mobility and scavenging of As, which in turn is important for understanding the formation and fingerprinting of mineral deposits as well as for the secure utilization of groundwater resources. [ABSTRACT FROM AUTHOR]

The combination of ozone and hydrogen peroxide (O3/H2O2), or the peroxone process, has often been used as an advanced oxidation process (AOP) in groundwater remediation and drinking water applications. This historical precedent sometimes leads to the misconception that H2O2 addition is required to achieve AOP conditions during ozonation. This is not the case for secondary or tertiary wastewater effluent applications, in which ozone reacts with abundant dissolved organic carbon (DOC) to generate hydroxyl radicals (∙OH). This study demonstrates the use of ozone with and without H2O2 addition to yield ∙OH exposures (up to 10−9 M-s) capable of achieving > 0.5-log10 attenuation of the industrial contaminant and probable human carcinogen 1,4-dioxane. This low molecular weight compound is commonly used as a surrogate when establishing AOP design criteria for potable reuse applications. DOC-normalized ozone doses (i.e., O3/DOC ratios) of ~ 1.0 and ~ 1.3 achieved 0.5-log10 attenuation of 1,4-dioxane with O3/H2O2 and O3, respectively. Also, a predictive model based on ∙OH exposure was accurate within approximately ± 10%. These results suggest that ozonation's role as an AOP, even in the absence of H2O2, should be acknowledged in regulatory frameworks to reduce unnecessary treatment redundancy and facilitate broader implementation of potable reuse. [ABSTRACT FROM AUTHOR]

Groundwater contamination caused by hydrocarbons is a common issue worldwide. Determining the volume of light non-aqueous phase liquids (LNAPL) that contaminate the subsurface environment is crucial for planning effective groundwater and soil remediation strategies, as well as determining the remediation endpoint. However, accurate approaches for quantifying the LNAPL volume in subsurface environments are scarce. To address this gap, we developed and tested a novel approach to quantify the volume of oil phase filling the soil pores. Our approach involves using a high-resolution technique, the laser induced fluorescence (LIF), to identify the presence of the oil phase, which was then correlated to total petroleum hydrocarbons (TPH) quantifications. For that, first, we obtained an empirical model to estimate the TPH present in the soil using fluorescence intensity and then, we converted the fluorescence intensity data in each log to equivalent TPH values. We used the model block approach, commonly used for ore resource estimation, to compute and discretize the volume of the aquifer contaminated by LNAPL into a set of blocks using the LIF data. Each block was assigned a mean TPH mass, which we used as a proxy for the LNAPL mass in the block. By summing the LNAPL mass in all blocks, we estimated the total LNAPL volume/mass in the investigated site. Our approach provides a simple and effective way to determine the amount of LNAPL contaminating the soil and groundwater, offering a new perspective for investigating hydrocarbon-contaminated sites. [ABSTRACT FROM AUTHOR]

This document discusses the issue of groundwater pollution, which poses a threat to ecosystems and human health. Groundwater pollution can come from natural sources or human activities such as agriculture and industry. Identifying the sources and mechanisms of pollution is crucial for prevention and mitigation efforts. The document highlights various studies from around the world that focus on groundwater contamination, including the evaluation of groundwater quality, assessment of health risks, and the development of remediation strategies. The research utilizes tools such as simulation models, remote sensing, and monitoring instruments to better understand and manage groundwater pollution. The goal is to protect and restore groundwater resources through effective prevention and remediation measures. [Extracted from the article]

The co‐occurrence of fluoride and arsenate in groundwater is a growing global concern owing to their synergistic adverse effect on human health. Thus, development of materials capable of capturing fluoride and arsenate simultaneously from aqueous medium is of much need. Moreover, it is a matter of great research importance to develop sustainable adsorbents by recycling solid wastes. Keeping this in mind, herein a novel pseudoboehmite nanoparticles (PBN) were synthesized by chemical valorization of disposable waste aluminium pan for simultaneous removal of fluoride and arsenate in aqueous medium. The physicochemical properties of the material were confirmed using analytical techniques such as XRD, BET, FT‐IR, FESEM etc. Batch study confirms the maximum monolayer adsorption of 90.10 mg g−1 and 94.84 mg g−1 of fluoride and arsenate respectively, which shows comparable affinity of the material for both contaminants. The selectivity of the adsorbent towards fluoride and arsenate was further evaluated by set of kinetic experiments in both single‐ion and mixture‐ion environment. The synthesis of pseudoboehmite nanomaterial using disposal waste Al pan and its high efficacy for removal of fluoride and arsenic even in presence of competing anionic environments provide a new direction of waste management for sustainable remediation of groundwater contaminants. [ABSTRACT FROM AUTHOR]

Iran is situated in a region with natural bitumen deposits and bitumen mines. This study compared the hydrogeochemical and isotopic composition of groundwater contaminated by abandoned bitumen mines (GCBM) with the deep formation water of oil reservoirs (FWOR). The GCBM was found to be dominated by Ca2+, Na+, SO42−, and Cl−, and is typically characterized by Ca–SO4 type water, in contrast to the Na–Cl type in the FWOR. The δ2HH2O and δ18OH2O isotopes were valuable tools to distinguish the groundwater sources, as the isotope signatures of GCBM and FWOR samples are markedly different. Ionic ratio diagrams, such as Na2+ vs. Cl−, Ca2+ vs. Cl−, and SO42− vs. Cl−, indicate that the groundwater chemistry in the study area is mainly influenced by gypsum and carbonate dissolution due to mining. The concentration of total petroleum hydrocarbons (TPH) ranged from 26.3 to 19,670 µg/L in the GCBM samples. This study confirmed unacceptable levels of groundwater contamination by TPH caused by seepage from abandoned bitumen mines and established a framework for future groundwater remediation efforts in the study area. [ABSTRACT FROM AUTHOR]

This study investigates the effects of nitrate exposure on the indigenous consortium mediated remediation of uranium-contaminated groundwater. Intermittent experiments reveal that high-nitrate concentrations hinder uranium reduction, whereas using glycerophosphate as carbon source, microbe could immobilize uranium by generating biomineralized precipitates with high crystallinity, and these precipitates exhibited better stability at high-nitrate concentration compared to those formed at low-nitrate condition. We also elucidated the mechanism of uranium removal by microorganisms under different conditions by analyzing changes in solution chemistry, products formed and microbial community structures. This work extends the scope for treating uranium-contaminated groundwater and is important for achieving long-term treatment of uranium contamination. [ABSTRACT FROM AUTHOR]

Groundwater contamination with per- and polyfluoroalkyl compounds (PFASs) has become a growing worldwide environmental issue. The current review comprehensively evaluates the global perspective of PFAS pollution in groundwater. Data from 224 recent research articles covering various land use and source types were reviewed, including industrial facilities, landfills, biosolids applications, and firefighting training sites. The bibliographic analysis shows an exponential increase in publications on PFAS pollution in groundwater in the last five years, with more than 50% coming from the USA, followed by Australia, Canada, China, and Sweden. The recent groundwater PFAS pollution research provides insight into the analytical techniques, absorbing materials, treatment strategies, field tests, and enhanced natural attenuation. Nevertheless, the current review identified significant research gaps in the areas of precursor characterization, subsurface behavior, model validation with field data, and long-term and sustainable solutions. Moreover, a global cross-disciplinary approach is required to reduce and regulate PFASs' risks to humans and the ecological system. This review presents a case study of PFASs in Saudi Arabian groundwater, revealing elevated levels of PFOA and PFOS and highlighting the need for region-specific studies and remediation strategies. The review results will guide global efforts to protect drinking water supplies from life-threatening contaminants. [ABSTRACT FROM AUTHOR]

This document is a summary of a special issue on hydrogeology, which is the study of groundwater and its interactions with the environment. It discusses various sub-disciplines within hydrogeology and their importance in addressing environmental issues such as water scarcity and pollution. The article also highlights eight significant research directions in modern hydrogeology, including groundwater formation, pollution, and remediation, as well as the management of groundwater resources. The document concludes by summarizing three review papers that cover topics such as water contamination, the use of carbon isotopes in studying the hydrological cycle, and the behavior of trace metals in coastal aquifers. It emphasizes the need for continued research, international collaboration, and action in the field of hydrogeology. [Extracted from the article]

Micron-scale zero-valent iron (ZVI)-based material has been applied for hexavalent chromium (Cr(VI)) decontamination in wastewater treatment and groundwater remediation, but the passivation problem has limited its field application. In this study, we combined aluminum chloride solution with ZVI (pcZVI-AlCl3) to enhance Cr(VI) removal behavior under aerobic conditions. The optimal pre-corrosion conditions were found to be 2.5 g/L ZVI, 0.5 mM AlCl3, and a 4 h preconditioning period. Different kinds of techniques were applied to detect the properties of preconditioned ZVI and corrosion products. The 57Fe Mössbauer spectra showed that proportions of ZVI, Fe3O4, and FeOOH in pcZVI-AlCl3 were 49.22%, 34.03%, and 16.76%, respectively. The formation of Al(OH)3 in the corrosion products improved its pHpzc (point of zero charge) for Cr(VI) adsorption. Continuous-flow experiments showed its great potential for Cr(VI) removal in field applications. The ZVI and corrosion products showed a synergistic effect in enhancing electron transfer for Cr(VI) removal. The mechanisms underlying Cr(VI) removal by pcZVI-AlCl3 included adsorption, reduction, and precipitation, and the contribution of adsorption was less. This work provides a new strategy for ZVI pre-corrosion to improve its longevity and enhance Cr(VI) removal. [ABSTRACT FROM AUTHOR]

Soil and groundwater contamination has always been a global concern. Contaminants are migrated and transformed in the soil and groundwater environments, which in turn pose potential environmental risks to humans. This paper describes four typical contaminants, including heavy metals, polycyclic aromatic hydrocarbons, microplastics, and perfluorinated and polyfluoroalkyl substances. Based on a systematic summary of the sources, hazards, and migration behaviors of these four contaminants, various existing remediation methods are analyzed, and the advantages and disadvantages of different methods are discussed. Finally, the future research prospects of soil and groundwater remediation are described, and the significance of the study of contaminant migration and remediation in the subsurface environment is emphasized. This research can help to provide theoretical and technical support for the study of contaminant migration and removal in soil and groundwater environments, and further improve the removal rate in actual contaminant sites. [ABSTRACT FROM AUTHOR]

The widespread occurrence of emerging brominated flame retardant tetrabromobisphenol S (TBBPS) has become a major environmental concern. In this study, a nanoscale zero-valent iron (nZVI) impregnated organic montmorillonite composite (nZVI-OMT) was successfully prepared and utilized to degrade TBBPS in aqueous solution. The results show that the nZVI-OMT composite was very stable and reusable as the nZVI was well dispersed on the organic montmorillonite. Organic montmorillonite clay layers provide a strong support, facilitate well dispersion of the nZVI chains, and accelerate the overall TBBPS transformation with a degradation rate constant 5.5 times higher than that of the original nZVI. Four major intermediates, including tribromobisphenol S (tri-BBPS), dibromobisphenol S (di-BBPS), bromobisphenol S (BBPS), and bisphenol S (BPS), were detected by high-resolution mass spectrometry (HRMS), indicating sequential reductive debromination of TBBPS mediated by nZVI-OMT. The effective elimination of acute ecotoxicity predicted by toxicity analysis also suggests that the debromination process is a safe and viable option for the treatment of TBBPS. Our results have shown for the first time that TBBPS can be rapidly degraded by an nZVI-OMT composite, expanding the potential use of clay-supported nZVI composites as an environmentally friendly material for wastewater treatment and groundwater remediation. [ABSTRACT FROM AUTHOR]

• Chemical-microbial coupled technology is promising for organic site remediation. • Controllable redox reactions are essential for coupling with microbial remediation. • Rational design of material, ROS generation, and degradation pathway is needed. • Progress on efficient and selective reductions of organic contaminants is reviewed. • Development of microorganisms for coupling with chemical remediation is introduced. Global environmental concern over organic contaminated sites has been progressively conspicuous during the process of urbanization and industrial restructuring. While traditional physical or chemical remediation technologies may significantly destroy the soil structure and function, coupling moderate chemical degradation with microbial remediation becomes a potential way for the green, economic, and efficient remediation of contaminated sites. Hence, this work systematically elucidates why and how to couple chemical technology with microbial remediation, mainly focused on the controllable redox reactions of organic contaminants. The rational design of materials structure, selective generation of reactive oxygen species, and estimation of degradation pathway are described for chemical oxidation. Meanwhile, current progress on efficient and selective reductions of organic contaminants (i.e., dechlorination, defluorination, -NO 2 reduction) is introduced. Combined with the microbial remediation of contaminated sites, several consideration factors of how to couple chemical and microbial remediation are proposed based on both fundamental and practical points of view. This review will advance the understanding and development of chemical-microbial coupled remediation for organic contaminated sites. [Display omitted] [ABSTRACT FROM AUTHOR]

A pumice–maghemite (P-maghemite) composite was developed using the chemical coprecipitation method with a 20% iron loading ratio by weight. The characterization of the composite using SEM and XRD indicated the effective loading and dispersion of nanoparticles on the surface of the developed base materials. Thereafter, in situ sequestration experiments were conducted in the laboratory for an arsenic-polluted aquifer system using two well-integrated permeable reactive barrier (PRB) modules filled with the developed composite. A vertical fixed-bed column setup was used for the columnar PRB, whereas a sand tank experimental setup was employed for the well-screen-integrated PRB; both PRB systems were fed by a synthetic solution representing the arsenic-contaminated groundwater. More than 99% arsenic removal was observed in the columnar PRB, with an average effluent concentration of 4 μg/L at the end of the experiment, which is well below the acceptable limit of drinking water for arsenic (<10 μg/L). Removal of arsenic by the 4-cm-wide well-screen-integrated PRB from 652 μg/L to less than 20 μg/L shows a great potential of the developed composite for arsenic remediation at slower groundwater flow rates. A maximum arsenic removal of 99% was attained at the start of the experiment, which decreased to 97% after 1 month of PRB operation. The effluent concentration of all other major ions also was reduced considerably in the PRB modules. The hydraulic conductivity of the developed media was reduced by 35% in the columnar PRB and by approximately 20% in the well-screen-integrated PRB. The high arsenic removal efficiency in continuous flow-through remediation systems indicates the applicability of the developed PRB system in in situ remediation of arsenic-contaminated groundwater. [ABSTRACT FROM AUTHOR]

In situ chemical injection technology is widely used in groundwater contamination remediation projects because of its high efficiency and low disturbance. Hydrodynamic dispersion is the basis for reagent transport in groundwater. Efficient diffusion and directional delivery processes of reagents in contaminated groundwater areas are key to controlling remediation efficiency. The complex subsurface environment and the limited efficacy of existing treatment technologies pose significant challenges for groundwater contamination remediation. Inhomo-geneous hydrodynamics in groundwater channels with heterogeneous media lead to significant uncertainties in the migration of reagents. Here, we conducted a systematic review to assess the nonideal transport behavior of remediation reagents under convection-dispersion, the blocking effect of heterogeneous media pores, and the kinetic process of reactive migration in saturated aquifers. The dilemma problems of low migration rate, unknown directionality, and nontargeted reactions encountered by reagents in porous groundwater media are systematically discussed from an environmental geological perspective. On this basis, we emphasize the strategies for the targeted control of reagent transport based on the regulation of the anthropogenic hydrodynamic flow field and density effects, an auxiliary strategy for regulating the target action of remediation to reduce nontarget reactions. Finally, future research needs are proposed to advance the development of engineering practices for green and sustainable in situ remediation technologies for contaminated groundwater. [ABSTRACT FROM AUTHOR]

Contamination of groundwater with fluoride represents a significant global issue, with high concentrations posing serious public health threats. While fluoride is a critical element in water, excessive levels can be detrimental to human health and potentially life-threatening. Addressing the challenge of removing fluoride from underground water sources via nanotechnological approaches is a pressing concern in environmental science. To collate relevant information, extensive literature searches were conducted across multiple databases, including Google Scholar, PubMed, Scopus, Web of Science, the American Chemical Society, Elsevier, Springer, and the Royal Society of Chemistry. VOS Viewer software version 1.6.20 was employed for a systematic review. This article delivers an exhaustive evaluation of various groundwater fluoride removal techniques, such as adsorption, membrane filtration, electrocoagulation, photocatalysis, and ion exchange. Among these, the application of nanoparticles emerges as a notable method. The article delves into nano-compounds, optimizing conditions for the fluoride removal process and benchmarking their efficacy against other techniques. Studies demonstrate that advanced nanotechnologies—owing to their rapid reaction times and potent oxidation capabilities—can remove fluoride effectively. The implementation of nanotechnologies in fluoride removal not only enhances water quality but also contributes to the safeguarding of human health. [ABSTRACT FROM AUTHOR]

As a green joint remediation technology after multi-phase extraction, monitored natural attenuation has gaps in chlorobenzene pollutants groundwater remediation projects, and its remediation effect and mechanism are still unclear. Based on the 727 d natural attenuation monitoring of pollution source after multi-phase extraction of groundwater in chlorobenzene contaminated sites, this study evaluated the natural attenuation capacity of chlorobenzene pollutants and discussed the mechanism of action from the perspective of practical engineering cases. The results show that the mass concentrations of 1,2-dichlorobenzene and 1,4-dichlorobenzene in shallow groundwater generally decline during 727 d of natural decay, but are not consistent with the one-order decay model. 1,2-dichlorobenzene and 1,4-dichlorobenzene were converted to chlorobenzene under the action of dechlorination bacteria at 416 d, and there was dechlorination of chlorobenzene to benzene at 529 d. Before the pilot test, Desulfomonile, Geobacter, Dehalobacter and Desulfovibrio are major potential dechlorine-degrading bacteria in the groundwater of the site. After the pilot test, the dominant bacterium has changed into Pseudomonas at 416 d. It is transformed into Dehalogenimonas, Pseudomonas, Desulfovibrio at 727 d. The degradation of dichlorobenzene to the chlorobenzene stage required more dechlorination bacteria, and the community diversity level was lower. When chlorobenzene degraded to benzene stage, the community structure was closer to the pollution-free state and the community diversity level was higher. After the pilot test, the bacterial community structure transformed to aerobic bacteria in 416 d, and to anaerobic bacteria after 416 d. This study can provide reference for economic and green remediation of chlorobenzene contaminated groundwater. [ABSTRACT FROM AUTHOR]

Chromate [Cr(VI)] contamination in groundwater is a global environmental challenge. Traditional elemental sulfur-based biotechnologies for Cr(VI) removal depend heavily on the synthesis of dissolved organic carbon to fuel heterotrophic Cr(VI) reduction, a bottleneck in the remediation process. Here we show an alternative approach by leveraging sulfur-disproportionating bacteria (SDB) inherent to groundwater ecosystems, offering a novel and efficient Cr(VI) removal strategy. We implemented SDB within a sulfur-packed bed reactor for treating Cr(VI)-contaminated groundwater, achieving a notable removal rate of 6.19 mg L−1 h−1 under oligotrophic conditions. We identified the chemical reduction of Cr(VI) via sulfide, produced through sulfur disproportionation, as a key mechanism, alongside microbial Cr(VI) reduction within the sulfur-based biosystem. Genome-centric metagenomic analysis revealed a symbiotic relationship among SDB, sulfur-oxidizing, and chromate-reducing bacteria within the reactor, suggesting that Cr(VI) detoxification by these microbial communities enhances the sulfur-disproportionation process. This research highlights the significance of sulfur disproportionation in the cryptic sulfur cycle in Cr(VI)-contaminated groundwater and proposes its practical application in groundwater remediation efforts.

Clay minerals are abundant on Earth and have been crucial to the advancement of human civilization. The ability of clay minerals to absorb chemicals is frequently utilized to remove hazardous compounds from aquatic environments. Moreover, clay-based adsorbent products are both environmentally acceptable and affordable. This study provides an overview of advances in clay minerals in the field of groundwater remediation and related predictions. The existing literature was examined using data and information aggregation approaches. Keyword clustering analysis of the relevant literature revealed that clay minerals are associated with groundwater utilization and soil pollution remediation. Principal component analysis was used to assess the relationships among clay mineral modification methods, pollutant properties, and the Langmuir adsorption capacity (Qmax). The results demonstrated that pollutant properties affect the Qmax of pollutants adsorbed by clay minerals. Systematic cluster analysis was utilized to classify the collected data and investigate the relationships. The pollution adsorption mechanism of the unique structure of clay minerals was investigated based on the characterization results. Modified clay minerals exhibited changes in surface functional groups, internal structure, and pHpzc. This review provides a summary of recent clay-based materials and their applications in groundwater remediation, as well as discussions of their challenges and future prospects. [ABSTRACT FROM AUTHOR]

pH-induced reactive transport in porous environments is a critical factor in Earth sciences, influencing a range of natural and anthropogenic processes such as mineral dissolution/precipitation, adsorption/desorption, microbial reactions, and redox transformations. These processes, pivotal in carbon capture and storage (CCS) applications to groundwater remediation, are determined by pH transport. However, the uncertainty in these macroscopic processes' stems from pore-scale heterogeneities and the high diffusion value of the ions and protons forming the pH range. While practical for field-scale applications, traditional macroscopic models often fail to accurately predict experimental and field results in reactive systems due to their inability to capture the details of pore-scale pH range. This study investigates the interplay between transverse mixing and pH-driven reaction in porous media. It focuses on how porous structure and flow rate affect mixing and chemical reaction dynamics. Utilizing confocal microscopy, the research visualizes fluorescently labeled fluids, revealing variations in mixing patterns from diffusive in homogenous to shear-driven in heterogeneous media. However, pH-driven reactions show a different pattern, with a faster reaction rate, suggesting quicker pH equilibration between co-flowing fluids than predicted by transverse dispersion or diffusion. The study highlights the unique characteristics of pH change in water, which significantly influences reactive transport in porous media. [ABSTRACT FROM AUTHOR]

Peroxymonosulfate (PMS, HSO5-) is an increasingly popular oxidant for groundwater remediation via in situ chemical oxidation (ISCO). However, it is desired to evaluate the effect of phosphate on the PMS oxidation of organics in detail due to the saline characteristics of groundwater. In this study, ofloxacin (OFX) as a typical antibiotic was chosen as a model pollutant. The results indicated that 64% of OFX was degraded by PMS in the presence of HPO42- (PMS/HPO42- system), and the efficiency increased from 64% to 80% when the HPO42- concentration was increased from 0.1 mol/L to 0.3 mol/L. The corresponding pseudo-first-order reaction constants were 0.0086 and 0.02 min-1, respectively. In comparison, PO43- and H2PO4- showed almost no reactivity. Electron spin response (ESR) analysis and quenching tests proved that SO4·- and 1O2 were the main oxidizing species for OFX degradation in PMS/HPO42- system. Hence, HPO42- was the most effective form in PMS activation and its performance was highly pH and ionic strength sensitive. Given the ambient pH and phosphate concentration in saline groundwater, a considerable amount of HPO42- can be produced, which then serves as a homogeneous PMS activator in ISCO process. This finding provides new insights into ISCO process using PMS. [ABSTRACT FROM AUTHOR]

Groundwater environments are complex, and traditional advanced oxidation technologies mainly based on free radicals have limitations such as poor selectivity and low interference resistance, making it difficult to efficiently degrade target pollutants in groundwater. Therefore, we developed a sludge-based biochar-supported FeMg-layered double hydroxide catalyst (BC@FeMg-LDH) for the catalytic degradation of 2, 4-dichlorophenol (2, 4-DCP) using persulfate (PDS) as an oxidant. The removal efficiency of the catalyst exceeded 95%, showing high oxidation activity in a wide pH range while being almost unaffected by reducing substances and ions in the environment. Meanwhile, under neutral conditions, the leaching of metal ions from BC@FeMg-LDH was minimal, thereby eliminating the risk of secondary pollution. According to quenching experiments and electron paramagnetic resonance spectroscopy, the main active species during BC@FeMg-LDH/PDS degradation of 2, 4-DCP is 1O2, indicating a non-radical reaction mechanism dominated by 1O2. Characterization techniques, including X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy, revealed that the carbonyl (C = O) and metal hydroxyl (M-OH) groups on the material surface were the main reactive sites mediating 1O2 generation. The 1O2 generation mechanism during the reaction involved ketone-like activation of carbonyl groups on the biochar surface and complexation of hydroxyl groups on the material surface with PDS, resulting in the formation of O2·− and further generation of 1O2. 1O2 exhibited high selectivity toward electron-rich organic compounds such as 2, 4-DCP and demonstrated strong interference resistance in complex groundwater environments. Therefore, BC@FeMg-LDH holds promising applications for the remediation of organic-contaminated groundwater. [ABSTRACT FROM AUTHOR]

Based on experimental results and self-consistent physical theory, a three-component description of nonlinear body waves in porous media is constructed. Applications of this result to two-component fluid flow in dynamic porous media and seismic wave propagation in multiphase porous media are presented. This description is important to petroleum reservoir simulation, groundwater hydrology, and seismic analysis of the earth. The two-body analogue of these results has been shown, in the past, to be inconsistent with the two-body linear models currently used by petroleum engineers and groundwater hydrologists. In seismic theory, simple linear models are generally used and much of the information obtained from the theory presented here is referred to as noise. The processes observed and described here have been patented and applied commercially to oil production and groundwater remediation. It is shown here that even if the correct nonlinear equations are used, three-component wave descriptions of porous media cannot be constructed solely from the equations of motion for the components. This is because of the introduction of the complexity of multiple scales into this nonlinear field theory. Information about the coupling between the components is required to obtain a physical description. It is observed that the fields must be coupled in phase and out of phase, and this result is consistent with the description of three- and n-body gravitational fields in Newtonian gravity and general relativity. [ABSTRACT FROM AUTHOR]

A new membrane-less bioelectrochemical reactor configuration was developed for contaminated groundwater remediation. The new bioelectrochemical reactor configuration was inspired by the utilisation of a permeable reactive barrier (PBR) configuration with no separation membrane. The corresponding reactive zones were created by using graphite granules and mixed metal oxide (MMO) electrodes to stimulate the reductive and oxidative biological degradation of chlorinated aliphatic hydrocarbons. In the present study, the PBR-like bioelectrochemical reactor has been preliminarily operated with synthetic contaminated groundwater, testing the reductive dechlorination activity on cis-dichloroethylene (cisDCE). Moreover, to assess the effects of competing anions presence for the electron donor (i.e., the cathode), the synthetic wastewater contained sulphate and nitrate anions. In the PBR-like reactor operation, nearly all cisDCE was removed in the initial sampling port, with only VC detected as the observable RD product. During the same biotic test of the PRB reactor, the presence of both the reductive dechlorination and anions reduction was confirmed by the complete nitrate reduction in the cathodic chamber of the PRB reactor. On the contrary, sulphate reduction showed a lower activity; indeed, only 25% of the influent sulphate was removed by the PRB reactor. [ABSTRACT FROM AUTHOR]

Nitrate pollution of water sources has been increasing due to the expansion of agriculture and human activities. The use of electrodialysis (ED) technologies has expanded significantly in recent years. In this study, an ED system with current circulation was built, and it was converted to electrodeionization (EDI) by adding resin to its dilute chambers. The EDI and ED systems by examining different operating parameters such as initial concentration, voltage, and flow rate, and their effects on the removal rate were compared. Flow rates of 10, 20, and 30 ml/min, voltages of 5, 10, and 15 V, and various nitrate concentrations (75, 100, 150, and 200 ppm) to assess the nitrate removal percentage were considered. The results showed that the average nitrate removal in the EDI process was significantly higher than in the ED process (P < 0.001) at all voltage, flow rate, and concentration levels. In the denitrification process by EDI, the osmotic property did not affect the membrane ion exchange process. The research results showed that the EDI process has better functionality to reduce nitrate concentration in water. The results also revealed that osmotic properties do not affect the membrane ion exchange process in the nitrate removal process by continuous electrodeionization. Additionally, the amount of nitrate removal increased with increasing voltage, while increasing the flow rate through the electro-ionization system decreased the amount of nitrate removal, thereby increasing the remaining nitrate. Furthermore, the highest rate of nitrate removal of 99.7% in the continuous electrodeionization system was achieved at the minimum initial concentration, minimum flow rate, and maximum voltage. As a fundamental technology for in situ remediation for groundwater contamination, the EDI process proved feasible and provided a foundation for further research. [ABSTRACT FROM AUTHOR]

The objective of this study was to explore the removal of nitrate ions from groundwater by employing dynamic permeable reactive barriers (PRBs) with A400-nZVI. This research aimed to determine the parameters of the barrier and evaluate its overall capacity to retain nitrate ions during percolation with a potassium nitrate solution. The process involves obtaining zerovalent iron (nZVI) nanoparticles, which were synthesized and incorporated onto an anionic resin support material (A400) through the reduction reaction of ferrous ions with sodium borohydride (NaBH4). This is achieved by preparing a ferrous sulfate solution, contacting it with the ion exchange resin at various solid–liquid mass ratios and gradually adding sodium borohydride under continuous stirring in an oxygen-free environment to create the A400-nZVI barrier. The results of the study, focusing on the development of permeable reactive barriers composed of nano zero-valent iron and ion exchangers, highlight the significant potential of water treatment processes when appropriately sized. The research specifically assesses the effectiveness of NO3− removal by using the A400-nZVI permeable reactive barrier, conducting laboratory tests that simulate a naturally stratified aquifer with high nitrate contamination. [ABSTRACT FROM AUTHOR]

The purpose of this manuscript is to present a review of laboratory experiments (including methodology and results) that use biochar, a specific carbon obtained by a pyrolysis process from different feedstocks, as an alternative material for heavy metal adsorption from groundwater. In recent years, many studies have been conducted regarding the application of innovative materials to water decontamination to develop a more sustainable approach to remediation processes. The use of biochar for groundwater remediation has particularly attracted the interest of researchers because it permits the reuse of materials that would be otherwise disposed of, in accordance with circular economy, and reduces the generation of greenhouse gases if compared to the use of virgin materials. A review of the different approaches and results reported in the current literature could be useful because when applying remediation technologies at the field scale, a preliminary phase in which the suitability of the adsorbent is evaluated at the lab scale is often necessary. This paper is therefore organised with a short description of the involved metals and of the biochar production and composition. A comprehensive analysis of the current knowledge related to the use of biochar in groundwater remediation at the laboratory scale to obtain the characteristic parameters of the process that are necessary for the upscaling of the technology at the field scale is also presented. An overview of the results achieved using different experimental conditions, such as the chemical properties and dosage of biochar as well as heavy metal concentrations with their different values of pH, is reported. At the end, numerical studies useful for the interpretation of the experiment results are introduced. [ABSTRACT FROM AUTHOR]

In this study, several adsorption models were studied to predict the adsorption kinetics of turbidity on an electro-generated adsorbent throughout the electrocoagulation remediation of real groundwater. A new design for an electrocoagulation reactor consisting of a finned anode positioned concentrically in a tube-shaped cathode was fabricated, providing a significant active area compared to its immersed volume. This work completed a previous electrochemical study through a deep investigation of adsorption technology that proceeded throughout the electrocoagulation reactor under optimal operating conditions, namely a treatment period of 2–30 min, a 2.3-Ampere current, and a stirring speed of 50 rpm. The one-, two-, and three-parameter adsorption models investigated in this study possess significant regression coefficients: Henry (R2 = 1.000), Langmuir (R2 = 0.9991), Freundlich (R2 = 0.9979), Temkin (R2 = 0.9990), Kiselev (R2 = 0.8029), Harkins–Jura (R2 = 0.9943), Halsey (R2 = 0.9979), Elovich (R2 = 0.9997), Jovanovic (R2 = 0.9998), Hill–de Boer (R2 = 0.8346), Fowler–Guggenheim (R2 = 0.8834), Dubinin–Radushkevich (R2 = 0.9907), Sips (R2 = 0.9834), Toth (R2 = 0.9962), Jossens (R2 = 0.9998), Redlich–Peterson (R2 = 0.9991), Koble–Carrigan (R2 = 0.9929), and Radke–Prausnitz (R2 = 0.9965). The current behavior of the adsorption–electrocoagulation system follows pseudo-first-order kinetics (R2 = 0.8824) and the Bangham and Burt mass transfer model (R2 = 0.9735). The core findings proved that an adsorption-method-based electrochemical cell has significant outcomes, and all the adsorption models could be taken into consideration, along with other kinetic and thermodynamics investigations as well. [ABSTRACT FROM AUTHOR]

[Display omitted] • PFAS concentrations in aqueous samples were measured at two landfills. • PFAS in municipal solid waste leachate was more variable than MSW ash leachate. • PFAS concentrations were stable within landfills (coefficient of variation < 50 %) • Leachate in uncovered trenches had the highest fluctuations. • PFAS fluctuations associated with alkalinity, total organic carbon, and ammonia. Studies of per- and polyfluoroalkyl substances (PFAS) fluctuations at landfills have focused on municipal solid waste (MSW) leachate. Few studies exist that evaluate fluctuations (defined by the coefficient of variation, CV) in MSW incinerator ash (MSWA) landfill leachate and that evaluate PFAS fluctuations in stormwater, groundwater, and treated liquids on-site. In this study, aqueous landfill samples (leachate, treated leachate, stormwater, gas condensate, ambient groundwater, and effluent from a groundwater remediation system) were collected from a MSW and an MSWA landfill geographically located within close proximity (less than 40 km). The objective of this study was to compare the leachate compositions between these two landfill types and to evaluate temporal variations. Results indicated that the CV of total detected PFAS concentrations in leachate was higher for the MSW landfill (CV = 43 %) compared to the MSWA landfill (CV = 16 %). The total detected PFAS concentration in MSW leachate samples (mean: 9641 ng/L) was higher than in MSWA leachate samples (mean: 2621 ng/L) (p < 0.05). Within a landfill, PFAS concentrations were correlated (r s > 0.6, p < 0.05) with alkalinity, total organic carbon (TOC), and ammonia. Results from the on-site leachate treatment system at the MSW landfill indicated reductions in COD, TOC, and ammonia; however, the ∑ 26 PFAS concentration increased 3 % after the treatment. Overall, results demonstrated that differences between landfill types and fluctuations in PFAS within landfills should be considered when designing landfill leachate collection and treatment systems to remove PFAS. The comparative analysis in this study can provide insights into optimizing leachate management for MSW and MSWA landfills. [ABSTRACT FROM AUTHOR]

The study of magnetically influenced flows in conjunction with non-Newtonian dusty fluids finds wide-ranging applications in minerals processing, environmental engineering, and biomedical sciences. These include, but are not limited to, wastewater management, soil remediation and groundwater treatment, removal of contaminants from water or soil, magnetic separation techniques, controlled and site-specific drug delivery, and biomedical diagnostic procedures. This research focuses on the dynamic behaviour of a conducting dusty fluid, modelled using the Casson framework, in the presence of a thermally active plate with ramped movement and the effects of a magnetic field. The model also incorporates several key physical phenomena, including thermal radiation, heat generation, and Newtonian heating wall conditions. To describe the time-dependent flow behaviour mathematically, partial differential equations are employed. Analytical solutions are derived using mathematical approach, notably the Laplace transform (LT). The results, including changes in flow profiles and various physical quantities due to various influencing factors, are depicted through graphs and tables, offering a clear visual representation of the findings. The research concludes that a higher thermal relaxation time parameter significantly improves thermal characteristics. Higher levels of particle concentration parameter correspond to slower fluid flow. Both the heat transfer rate and shearing stress on the plate exhibit temporal variations for a range of physical parameters. The particle concentration parameter has a notable impact on thermal transmission. The study's findings may be applied in climate modelling, weather prediction, contaminant transport, and studying phenomena such as dust storms, air pollution, and dispersion of volcanic ash clouds. [ABSTRACT FROM AUTHOR]

Various soilless substrate components have been evaluated for many years to identify sustainable resources that do not negatively impact plant growth. Biochar is a carbon-based material that has been evaluated for use as an alternative aggregate in peat-based soilless substrates. In addition, the use of carbon adsorption for compound removal is widely used in groundwater remediation, municipal water filtration, and volatile organic compounds. Experiment one aimed to determine the impact of coarse biochar (<6 mm) on paclobutrazol efficacy when incorporated at 15% or 30% by volume in a peat-based substrate when compared with a perlite-amended substrate at the same incorporation volumes. In Expt. 1, a single paclobutrazol drench application of 0, 0.5, 1.0, 2.0, and 4.0 mg·L21 was applied to 'Princettia Red' and 'Princettia White' poinsettias (Euphorbia pulcherrima × Euphorbia cornastra). In Expt. 2, two different biochar particle sizes of coarse (<6 mm) and extra coarse (>6 mm) were examined at the same incorporation volumes as Expt. 1 and compared with a perlite-amended substrate at the same incorporation volumes. However, during Expt. 2, continual drench applications at times of irrigation of 0.0, 6.25, 12.5, 25.0, 50, and 100 lg·L21 (ppb) paclobutrazol were applied to pansy (Viola ×wittrockiana) 'Matrix Blue Blotch' and begonia (Begonia ×hybrida) 'Big Red Bronze Leaf'. The efficacy of paclobutrazol drenches for controlling growth in all species was unaffected by the substrate composition regarding aggregate type or aggregate incorporation rate. Thus, even though biochar is often used for bioremediation and wastewater treatment, it did not negatively impact the efficacy of paclobutrazol drenches at the concentrations used. This research suggests that when biochar is used as an amendment to peatmoss it will not influence paclobutrazol drench efficacy when incorporated up to 30% by volume for the examined species. [ABSTRACT FROM AUTHOR]

To enable proper remediation of accidental groundwater contamination, the contaminant plume evolution needs to be accurately estimated. In the estimation, uncertainties in both the contaminant source and hydrogeological structure should be considered, especially the temporal release history and hydraulic transmissivity. Although the release history can be estimated using geostatistical approaches, previous studies use the deterministic hydraulic property field. Geostatistical approaches can also effectively estimate an unknown heterogeneous transmissivity field via the use of joint data, such as a combination of hydraulic head and tracer data. However, tracer tests implemented over a contaminated area necessarily disturb the in situ condition of the contamination. Conversely, measurements of the transient concentration data over an area are possible and can preserve the conditions. Accordingly, this study develops a geostatistical method for the joint clarification of contaminant plume and transmissivity distributions using both head and contaminant concentration data. The applicability and effectiveness of the proposed method are demonstrated through two numerical experiments assuming a two-dimensional heterogeneous confined aquifer. The use of contaminant concentration data is key to accurate estimation of the transmissivity. The accuracy of the proposed method using both head and concentration data was verified achieving a high linear correlation coefficient of 0.97 between the true and estimated concentrations for both experiments, which was 0.67 or more than the results using only the head data. Furthermore, the uncertainty of the contaminant plume evolution was successfully evaluated by considering the uncertainties of both the initial plume and the transmissivity distributions, based on their conditional realizations. [ABSTRACT FROM AUTHOR]

Groundwater is an important part of the water resources, crucial for human production and life. With the rapid development of industry and agriculture, organic pollution of groundwater has attracted great attention. Enhanced in-situ bioremediation of groundwater technology has gradually gained attention because of its high efficiency and low environmental impact. Bioremediation agents are crucial for bioremediation technology. In this review, bioremediation agents were classified into three categories: biological nutrition agents, slow-release agents, and microbial agents. Biological nutrition agents are a specific mixture of mineral salt and carbon source; slow-release agents may contain mineral salt, carbon source, pH buffers, and oxygen-releasing material and microbial agents with specific microbial culture. By adding bioremediation agents to the polluted sites, they can improve population density and degradation efficiency for microbial degradation of pollutants. To assist future development and application of bioremediation agents, the development of different agents in laboratory and commercial to date was retrieved online via publisher sites and cooperation case studies. The data collected were analyzed and reviewed, as well as application and remediation effects of enhanced in-situ bioremediation agents were summarized. Current studies mainly focus on laboratory development and experiments, while field tests and remediation effects between different agents are of less concern. Further study may focus on developing new materials, especially coating or loading materials, and systematic evaluation of different agents, considering both laboratory research and on-site experiments, in order to improve the efficiency of in situ organically contaminated groundwater bioremediation. [ABSTRACT FROM AUTHOR]